1. Field of the Invention
The present invention relates to backlight units, and more particularly, to a backlight unit capable of preventing luminance deviation, and a liquid crystal display device including the backlight unit.
2. Description of the Related Art
A liquid crystal display (“LCD”) device has gradually extended its application range due to light weight, thin thickness and low consumption power driving. The LCD device applies an electric field to a liquid crystal material having dielectric anisotropy injected between two substrates and controls the amount of light transmitted into the substrates by adjusting the intensity of the electric field, thereby displaying desired images.
Since an LCD panel of the LCD device is a non-luminous element that cannot emit light by itself, the LCD device includes a backlight unit for providing light to the LCD panel.
A light emitting diode (“LED”) used for the backlight unit has long life span, fast lighting speed, low power consumption and high impact resistance, compared to a cold cathode fluorescent lamp (“CCFL”), etc. Moreover, the LED is suitable to make the backlight unit relatively small and thin.
FIG. 1 is a plan view illustrating a light source substrate of a conventional LCD device of the prior art. Referring to FIG. 1, LEDs 16 are mounted on a light source substrate 18 supplying control signals or driving voltages to the LEDs 16. The light source substrate 18 may be bonded or adhered, such as by a double coated tape, etc., to a light guide plate (not shown) for guiding incident light from the LEDs 16 toward an LCD panel (not shown).
Since the adhesion of the light source substrate 18 to the light guide plate may be weakened by heat of the LEDs 16 generating the light, the adhesive force between the light guide plate and the light source substrate 18 deteriorates and there occurs a separation region between the light guide plate and the LEDs 16. Furthermore, if vibrations or shocks are applied from the exterior, the separation region may also occur between the light guide plate and the LEDs 16. Since light emitted through the separation region is directly incident on the LCD panel, a luminance deviation occurs in that the light emitted through the separation region seems to be relatively brighter than the light emitted through the other regions.
Moreover, since a separation distance between the light guide plate and the light source substrate 18 may vary due to an assembly deviation between workers during an attachment process of the light guide plate and the light source substrate 18, it is difficult to ensure the uniform luminance characteristic.
Referring again to FIG. 1, a light amount “H” incident on the light guide plate overlapping emitting surfaces of the LEDs 16 is greater than a light amount “L” incident on the light guide plate not overlapping the emitting surfaces of the LEDs 16. Therefore, the incident surface of the light guide plate overlapping the emitting surfaces of the LEDs 16 seems to be relatively brighter than the surface not overlapping the emitting surfaces of the LEDs 16.